ELECTRIC HEATER

Abstract: A panel heater (2) comprises a metal casing (4) having respective spaced apart front and rear walls (6, 8) respective side walls (10, 12) and respective top and bottom walls (14, 16). The top and bottom walls include a plurality of slots (54) arranged in groups. A heating element is secured to the rear face of the front wall (6) and is arranged in operation to conduct heat to the front wall (6) which, in turn, radiates heat into a room in which the heater is disposed. Additionally, air can flow into the casing (4) via slots (54) in bottom wall (16) and over a rearwardly facing face of the heating element which heats the air. The heated air flows out of the casing, via slots (54) in the top wall (14), and into the room as convected heat. The construction of the heater (2) is arranged to maximise the transformation of electrical energy into thermal energy dissipated as useful heat within the room.

Description: ELECTRIC HEATER The invention relates to an electric heater. Known electric heaters for emitting both radiant and convected heat comprise a hollow casing which includes spaced apart front and rear walls, and top and bottom walls which have openings therethrough. An electrical resistance heating element is positioned between the front and rear walls and is arranged to radiate heat to the front wall which, in turn, radiates heat into a room in which the heater is placed. Additionally, air entering the casing through the openings in the lower wall passes over the heating element and is warmed thereby before passing through the openings in the top wall into the room. The known heater described is very inefficient in terms of transforming electrical energy into thermal energy. One of the reasons for this inefficiency is the fact that, not only does the heating element radiate heat to the front wall, but also to the rear wall so that the rear wall becomes hot. When the heater is mounted on a wall in a room, the rear wall of the heater will radiate and/or conduct heat to the room wall which will become heated and, since the room wall will have a high specific heat capacity, much heat (and energy) is lost to the room wall. It is an object of the invention to alleviate problems associated with known electric heaters. According to the invention, there is provided an electric heater including a front panel and a rear panel between which an internal area of the heater is defined, wherein a heating element is held against the rear face of the front panel so that, in use, the front panel becomes heated so as to provide radiant heat and air can flow within the internal area over the heating element in order to provide convected heat. Preferably, the heating element includes a resistive element arranged to become heated when a current passes therethrough. Said resistive element preferably comprises a metal or metals. Preferably, said resistive element comprises an alloy of, for example, iron, chromium and aluminium. Said resistive element preferably comprises a wire. Said resistive element may include individually operable resistive elements of different resistances. Said heating element preferably comprises a first electrically insulating member which is arranged to space the resistive element from the rear face of the front panel. Said first electrically insulating member is preferably in the form of a panel. Said panel preferably overlies the resistive element. Said panel is preferably made of a sheet material. Said panel is preferably made of a flexible and/or elastic material. Said resistive element is preferably secured to the first electrically insulating member, for example by adhesive means. Said heating element preferably also includes a second electrically insulating member, suitably in the form of a panel. Said resistive element is preferably secured to the second insulating member, for example by adhesive means. Said resistive element is, preferably positioned between said first and second electrically insulating members. Said first and/or said second electrically insulating members may have an electrical resistivity at 23°C of greater than 0.1 Ohms.cm. Preferably, the resistivity is greater than 1.0 Ohms.cm and is, more preferably, greater than 5.0 Ohms.cm. Said first and/or said second electrically insulating members are preferably thermally conductive. The thermal conductivity of the members may be greater than 0.05 Wm' 1 K- 1 . Said first and/or said second electrically insulating members preferably can resist temperatures of at least 500°C and, more preferably, of at least 600°C. Said first and/or second electrically insulating members preferably independently have a width of at least 0.1 mm and, more preferably, of at least 0.15 mm. The width is preferably less than 20 mm, more preferably less than 10 mm. Said first and/or second electrically insulating members are suitably made of a micanite material. Said heating element is preferably held against the rear face of the front panel by adhesive means. A mechanical means for holding the heating element in position may also be provided. Preferably, the heater includes upper and lower openings from and to the internal area thereof, whereby air can flow to provide convected heat. Preferably, no air passage is defined between the first electrically insulating member and the rear face of the front panel, whereas an air passage is defined between a rearwardly facing portion of the heating element and the rear panel. The lower openings preferably are elongate and have an axis of elongation. Side walls which define the respective openings are preferably substantially linear and suitably extend substantially parallel to the axis of elongation. End walls which define the openings are preferably curved. Said end walls are preferably concave so the ends of the openings are, therefore, convex. The openings are preferably symmetrical about their respective axes of elongation and, preferably, about respective axes perpendicular to the axis of elongation. Said openings may have a length in the range 5 mm to 50 mm, preferably in the range 7 mm to 25 mm and, more preferably, in the range 10 mm to 20 mm. The width of the openings may be in the range lmm to 20 mm, preferably in the range 2mm to 10mm, more preferably in the range 2 mm to 5mm. Said lower openings are preferably defined in a lower wall of the heater. Said lower wall is preferably substantially planar. Said lower wall is preferably arranged, in use, with its main plane substantially parallel to the ground. Said lower openings are preferably grouped together, with at least two spaced apart groups of openings being provided in the lower wall. Openings in each group are preferably substantially identical. The elongate axes of openings in each group preferably extend parallel to one another. Said upper openings of the appliance may independently include any features of the lower openings as described above. Upper openings and lower openings are preferably substantially identical. Said upper openings are preferably defined in an upper wall of the appliance. Said upper wall is preferably substantially planar. The planes of the upper and lower walls preferably extend substantially parallel to one another. Axes of elongation of lower openings are preferably not parallel to axes of elongation of upper openings. Axes of elongation of lower openings preferably extend transversely to axes of elongation of upper openings. Axes of elongation of lower openings preferably extend at an angle of about 90° to axes of elongation of upper openings. Axes of elongation of lower openings preferably extend transversely to a rearwardly facing face of the heating element. Preferably the front and/or rear panels are substantially planar and the axes of elongation of lower openings extend transversely, suitably at an angle in the range 30° to 60°, preferably at 45°, to the planes. The total area of the lower openings is preferably less than the total area of the upper openings. The total area of the lower openings may be less than 85%, preferably less than 80%, more preferably less than 75% of the area of the upper openings. The total area of the lower openings may be at least 40%, preferably at least 50%, more preferably at least 60% of the area of the upper openings. The lower and upper openings are preferably arranged to cause air flowing within the internal area of the heater to create a vortex. Securement means is preferably provided for securing the heater to an upright surface, for example a wall. Alternatively and/or additionally, the appliance may be arranged to be free-standing. Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view, partly in cross- section, of a panel heater; Figure 2 is a cross-section along line II-II of Figure 1; Figure 3 is a cross-section along line III-III of Figure 2, showing a lower part of the panel heater; Figure 4 is a plan view, partly in cross-section, of a heating element of the panel heater; Figure 5 is a cross-section along line V-V of Figure 4 (with details omitted in the interest of clarity) ; Figure 6 is a detailed view of the area within region VI of Figure 5; Figure 7 is a plan view of a front panel of the heater; Figure 8 is a plan view of a rear panel of the heater; Figure 9 is a plan view showing two slots of the front panel; - 1 - Figure 10 is a cross-section along line X-X of Figure 8; and Figure 11 is a plan view, partly in cross-section, of an alternative heating element of the panel heater. In the figures, like or similar parts are annotated with the same reference numerals. Referring to Figure 1, the panel heater 2 comprises a metal casing 4 having respective spaced apart front and rear walls 6, 8, respective side walls 10, 12 and respective top and bottom walls 14, 16. The top and bottom walls include a plurality of slots 54 arranged in groups. A heating element is secured to the rear face of the front wall 6 and is arranged in operation to conduct heat to the front wall 6 which, in turn, radiates heat into a room in which the heater is disposed. Additionally, air can flow into the casing 4 via slots 54 in bottom wall 16 and over a rearwardly facing face of the heating element which heats the air. The heated air flows out of the casing, via slots 54 in the top wall 14, and into the room as convected heat. The construction of the heater 2 is arranged to maximise the transformation of electrical energy into thermal energy dissipated as useful heat within the room. The heater 2 is described is greater detail below. The element 20 of the heater, shown in Figures 4 to 6, comprises electrical resistance wire 22 located between sheets 24, 26 formed from a material which is electrically insulating but is reasonably thermally conductive. Electrical connectors 24, 26 are provided for connecting a power supply to the wire 22. The resistance wire 23 is suitably made of an alloy of iron, chromium and aluminium. One such wire is sold by IMI Scott Limited under the Trade Mark CROMALOY A. The properties and lenσth of the wire used are selected according to the heat output reguired. For a 500 W heater, a 5.95 m length of 0.30 mm diameter wire having a resistivity of 18.86 ohms/metre may be used. The resistance wire is arranged in the convoluted pattern as shown in Figure 4, so that the heating of the front panel will be as uniform as possible. A thermostat is provided for controlling the supply of current to the resistance wire 23. The sheets 24, 26 of the element 20 are formed from 0.2 mm thick sheets of PERMIC 505.3 (Trade Mark) which is a bonded multi-layer rigid micanite material obtainable from COGEBI of Huysmanslann 65, B1651 LOT, Belgium. The material is able to resist 700°C in continuous service and can intermittently be raised to 800°C and beyond, without adverse effect. The electrical resistivity of the material at 23°C is greater than 10 ohms.cm. The material also has reasonable thermal conductivity of about 0.3 Wm' 1 K *1 . The resistance wire 23 and sheets 24, 26 are held in position using respective polyester carrier sheets 28, 30 each of which is coated on both sides with an acrylic based adhesive material 32. The sheets are preferably supplied in continuous sheet or tape form. A suitable material can be obtained from Nitto Limited under the code number 5033X. The element 20 may be made as follows: Carrier sheet 28 is secured by means of its lower adhesive layer 32 to sheet 26. Then, wire 23 which has been wound into the desired configuration in a jig, is applied to the upper adhesive layer 32 of carrier sheet 28. The carrier sheet 30 is then secured by means of its upper adhesive layer 32 to the sheet 24 and then the lower adhesive layer is pressed against the wire 23. An upper carrier sheet 34 is secured by means of its lower adhesive layer 32 to the sheet 24. The upper adhesive layer 32 of the carrier sheet 34 may then be adhered to the rear face of the front wall 6 of the casing in order to secure the element in position. The casing 4 is constructed using a front panel 40, shown in Figure 7, and a rear panel 42, shown in Figure 8. Referring to Figure 7, the front panel 40 has respective upper and lower side portions 44, 46 and respective lateral side portions 48, 50 arranged around area 52 which forms the front wall 6 of the casing. The upper side portion 44 includes a lip portion 47 and a face portion 49. The upper and lower side portions 44, 46 are provided with a series of slots 54 which are arranged in three groups 56, 58, 60 in the lower side portion 46 and in five groups 62, 64, 66, 68, 70 in the upper side portion 44. The lateral side portion 48 is provided, towards its lower end, with openings 72, 74 to receive a control switch and supply cable. The upper and lower side portions include openings 76 for receiving rivets. An opening 78 is provided in the upper portion for a neon operating light. The panel 40 is formed from a single sheet of steel and is arrranged as follows: The upper and lower side portions 44, 46 are bent inwardly through 90°; the lip portion 47 of the upper portion 44 is bent inwardly through 90° relative to the face portion 49; and the lateral side portions 48, 50 are bent inwardly through 90°. When so arranged panel 40 may be secured to rear panel 42. Rear panel 42, shown in Figure 8, is of similar construction to panel 40 in that it includes upper and lower side portions 80, 82 and lateral side portions 84, 86, but the dimensions of the panel 42 are such that its side portions, when bent inwardly through 90°, can be located within side portions defined by the front panel 40. Additionally, the upper and lower side portions 80, 82 are provided with recesses 88,90, so as not to obstruct the slots 54 when the two panels 40, 42 are assembled together and, furthermore, lateral side portion 84 is provided with a slot 92 in order to accommodate the switch and supply cable. Secured on the interior surface of the rear panel 42, by means of projecting parts 96 (Figure 10) , are spaced apart elongate supports 94 which are conveniently formed from pressed strip material which is formed to "V"-section. The arrangement and number of slots 54 in the upper and lower side portions 44, 46 are selected in order to control the convected heat emitted by the panel heater. Suitably, the amounts of radiated and convected heat emitted by the heater are substantially egual. Each of the slots 54 is arranged as shown in Figure 9. The slots are generally rectangular, but have radiussed ends. The elongate axes of the slots are inclined at 45° to the elongate axes of the top and bottom walls 14, 16 of the panel. The length "x" of each slot is 15 mm and the width "y" is 3 mm. The elongate axes of the slots are parallel to one another and the mid-points of adjacent elongate axes are spaced from one another by a distance "z" of 7.3 mm. - li ¬ lt should be noted that, when the upper and lower side portions 44, 46 of the front panel 40 are bent inwardly through 90°, the elongate axes of the slots 54 in the lower side portion 46 extend at an angle of 90° to the elongate axes of the slots 54 in the upper side portion 44. As mentioned above, the slots 54 are arranged into groups. There are twenty-one identical slots 54 in each respective group 56, 58, 60 of the lower side portion 46 which forms bottom wall 18 of the panel; and nineteen identical slots 54 in each respective group 62, 64, 66, 68, 70 of the upper side portion 44 which forms the upper wall 14 of the panel. Thus, the open area defined by the slots in the bottom wall 18 is about 66% of the open area defined by the slots in the top wall 16. The panel heater is assembled by adhering element 20 to the rear face of the front wall 6, arranging the control switch, supply cable and operating light in position and then rivetting the front and rear panels 40, 42 together. When so disposed, the elongate supports 94 lie in close proximity to the rearwardly facing face 98 of the element 20 so as to provide a mechanical means of locating the element in position in the event of failure of the adhesive. In use, power is supplied to the wire 22 of the element 20 and the wire heats up. Heat is conducted from the wire into sheets 24, 26. Heat from sheet 24 is conducted to front wall 6 of the casing which then radiates the heat outwardly. Air flows into the casing via openings 54 in the bottom wall 16 and over the sheet 26 before exiting through slots 54 in the top wall 14. As the air passes through the casing, it creates vortexes which result in the velocity of the air through the casing being greater than the velocity of convected air when vortexes are not created. The air flowing over the element removes heat from the element at a relatively rapid rate such that little heat is absorbed by the rear wall 8 of the casing and, conseguently, little heat is lost to a wall of a room upon which the heater may be mounted. When wire 22 of the element 20 heats up, it expands slightly. It is important for spaced apart elongate parts 25 of the element not to move laterally to any appreciable degree since there will be a risk that such movement may result in the parts fusing together which will affect the effective resistance of the wire 22. As shown in Figure 6, the lateral movement is restricted by sheets 32 being slightly curved around the wire 22. The heater 2 is intended to be mounted on a wall and, to this end, rear wall 8 is suitably provided with a pair of keyhole apertures near its upper edge and a part sheared flap 100 near its lower edge which can be bent through 180° so that it projects below the heater. The flap is apertured to receive a securing screw. Various different sizes of panel heaters may be made with heating elements of varying powers. The heater described is a 500W heater. Heaters of power as little as 350W or as great as 1200W may be made. Where a relatively high power heater is reguired (e.g. 900W or above) , the construction of the heating element may generally be as described above, except that two separate lengths of 110, 112 (Figure 11) of resistance wire of different electrical resistance may be incorporated. In Figure 11, wire 110 is shown in dashed lines and wire 112 is shown in full lines, in the interests of clarity. Separate pairs of electrical connectors 114, 116 are provided for the respective wires. The wires 110, 112 may be made from CROMALOY as described above. The lengths of the wires 110, 112 are different - wire 110 has a length of 7.095 m, whereas wire 112 has a length of 7.825 m. Thus, the resistance of wire 110 is less than wire 112 and, therefore, there will be a higher dissipation of heat in wire 110 compared with wire 112. A thermostat 118 is connected in series with wire 110 and this is mounted so that it is responsive to the temperature of wire 110. A suitable thermostat is that sold by Microtherm Limited under the type number Bll. In use, when the heater is first connected to a source of supply both wires carry current so that rapid heating of the front half of the heater is obtained. When the wire 110 attains a temperature determined by the thermostat, the latter opens to disconnect the heater wire 110 from the source of supply. The heater wire 112, however, continues to carry current and, therefore, dissipates heat. With the arrangement described, therefore, the full heating effect is obtained very quickly after the supply is turned on but excessive heating is avoided by reducing the heat dissipated when the heater has reached its correct working temperature. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims: CLAIMS 1. An electric heater including a front panel and a rear panel between which an internal area of the heater is defined, wherein a heating element is held against a rear face of the front panel so that, in use, the front panel becomes heated so as to provide radiant heat and air can flow within the internal area over the heating element in order to provide convected heat. 2. A heater according to Claim 1, wherein said heating element comprises a first electrically insulating member which is arranged to space a resistive element from the rear face of the front panel. 3. A heater according to Claim 2, wherein said first electrically insulating member is in the form of a panel. 4. A heater according to Claim 2 or Claim 3, wherein said resistive element is secured to the first electrically insulating member by adhesive means. 5. A heater according to any of Claims 2 to 4, including a second electrically insulating member to which the resistive element is secured. 6. A heater according to Claim 5, wherein said resistive element is positioned between said first and second electrically insulating members. 7. A heater according to any of Claims 2 to 6, wherein said first and/or said second electrically insulating members have an electrical resistivity at 23°C of greater than 0.1 Ohms.cm. 8. A heater according to any of claims 2 to 7, wherein the thermal conductivity of said first and/or said second electrically insulating members is greater than O.OSWπf'K "1 . 9. A heater according to any preceding claim, wherein said heating element is held against the rear face of the front panel by adhesive means. 10. A heater according to any preceding claim, including upper and lower openings from and to the internal area, whereby air can flow to provide convected heat. 11. A heater according to Claim 10, wherein said upper and lower openings are elongate. 12. A heater according to Claim 11, wherein axes of elongation of respective upper and lower openings extend transversely to one another. 13. A heater according to any of Claims 10 to 12, wherein the total area of the lower openings is less than the total area of the upper openings. 14. A heater according to Claim 13, wherein the total area of the lower openings is less than 75% of the total area of the upper openings. 15. A heater according to any of Claims 10 to 14, wherein said upper and lower openings are arranged to cause air flowing within the internal area to create a vortex.

Inventors: MARSDEN BARRY JAMES, MARSDEN, BARRY, JAMES
Applicants: MARSDEN BARRY JAMES, MARSDEN, BARRY, JAMES
Application year: 1994
Main classification: F24D13
IPC codes: F24D13